I was wondering if anyone has an idea how I can calculate RPM from pulley size. Specifically, I want to mount an electric motor to an old cement mixer. The main wheel on the mixer is 64inches in circumference. I have several electric motors, most 1725 RPM, but I do have one around 1125. Rather than shoot in the dark, I'm hoping someone has a formula for calculating RPM on the main wheel based on a motor pulley size and RPM. The mixer wheel is on a 1 to 1 gear ratio with the mixer drum. Hope this makes sense. Thanks.